1. Field of the Invention
The present invention relates to a method for producing a zinc oxide single crystal.
2. Description of the Related Art
Zinc oxide (ZnO) is a material used in a broad range of applications such as pigments, cosmetics, piezoelectric devices, varistors, and gas sensors, and in recent years it has been expected that zinc oxide can be applied to light emitting devices such as light emitting diodes (LEDs) due to its wide band gap and excellent optical properties.
A hydrothermal synthesis method (e.g., Patent Document 1 (JP2004-315361A)) and a liquid phase epitaxial method (LPE method) (e.g., Patent Document 2 (WO2007/100146) are known as methods for growing zinc oxide single crystals. Although the productivity of the hydrothermal synthesis method is comparatively high, and zinc oxide single crystals produced thereby are commercially available, the hydrothermal synthesis method is problematic in that high-concentration doping required for controlling electrical properties is difficult. On the other hand, the LPE method, while it enables high-concentration doping, is problematic in that the productivity is low and, further, harmful PbO and Bi2O3 need to be used as fusing agents.
Meanwhile, as a technique that enables formation of a dense ceramic film at room temperature, an aerosol deposition method (hereinafter also referred to as an AD method) has recently been attracting attention. It is considered that, in this AD method, when raw material particles that have been formed into an aerosol collide with a substrate at high speed, the particles plastically deform due to the generated stress, and a film is formed by the mechanochemical reaction between the activated particle surface and the substrate. However, it is known that with the AD method the reproducibility of film formation is generally low. One reason for this is that the aerosol concentration is affected by, for example, a subtle change in particle size distribution and is unlikely to be stable (see Patent Document 3 (JP4371884B)). Also, it is known that with the AD method the ability of particles to plastically deform during film formation is dependent on, for example, the particle diameter and the components of the raw material (Non-Patent Document 1 (supervised by Jun Akedo, “Aerosol Deposition (AD) Process: The Basic and Applications—Novel Ceramic Coating Technology with Room Temperature Impact Consolidation (RTIC)”, CMC Publishing Co., Ltd., published on Jun. 30, 2008, pp. 45-46)). In particular, with zinc oxide, there is a problem in that the ability of particles to plastically deform is poor, and the reproducibility of the AD deposition is low.